Determining structural tomographic properties of a geologic formation

Abstract

A variable-frequency light source is configured to emit a light beam and modulate a frequency of the light beam. A fiber optic cable is attached to the variable frequency light source. The fiber optic cable is configured to receive the light beam at an inlet and pass the light beam to an exit. Multiple optical detectors are attached to the fiber optic cable. Each of the optical detectors is configured to detect a specified frequency of light that is backscattered through the fiber optic cable. An actuation mechanism is attached to the fiber optic cable. The actuation mechanism is configured to deform the fiber optic cable in response to a stimulus.

What is claimed is: 
     
       1. A distributed geophone system comprising:
 a plurality of sub-surface detection devices installed within a plurality of boreholes, each of the plurality of sub-surface detection devices comprising:
 a variable frequency light source configured to emit a light beam and modulate a frequency of the light beam; 
 a fiber optic cable attached to the variable frequency light source, the fiber optic cable configured to receive the light beam; 
 a plurality of optical detectors attached to the fiber optic cable, each of the optical detectors configured to detect a specified frequency of light that is backscattered through the fiber optic cable; 
 an actuation mechanism attached to the fiber optic cable, the actuation mechanism configured to deform the fiber optic cable in response to a stimulus; and 
 
 a central processing center configured to monitor and store data produced by the plurality of sub-surface detection devices. 
 
     
     
       2. The system of  claim 1 , wherein the actuation mechanism comprises:
 an antenna configured to detect changes in an electromagnetic field; and 
 an electromechanical transducer that is connected to the antenna, the electromechanical transducer configured to deform the fiber optic cable in response to detecting changes in the electromagnetic field. 
 
     
     
       3. The system of  claim 1 , wherein the actuation mechanism comprises:
 a hydrophilic gel configured to expand in the presence of moisture; and 
 a diaphragm connected to the hydrophilic gel and the fiber optic cable, wherein an expansion in the hydrophilic gel induces the diaphragm to deform the fiber optic cable.